Process of producing waterproof characters upon paper.



. visible by being properlydeveloped.

, 5 again invisible when the paper is dry. I

' With these andother objects in view, the invention fjconsists in the practice of the process UNITED I STATES OTTO MEYER, OF R PATENT orrrron.

ronMoND, VIRGINIA.

Specification of Letters Patent.

Patented Sept. 17, 1907.

Application filed August 25. 1906. Serial No. 332,056.

To all whom it may concern: I

Be it known that I,;Or'rp MEYER, a citizen of the United States, residing at Richmond, in the county of Henrico and State of Virginia, have invented certain new and useful Improvements in Processes of Producing Waterproof Characters Upon Paper; and .I do hereby declare the following to be a full, clear, and exact description ofthe invention, such as will enable others skilled in the art to which it appertains to make and use the same. y This invention relates to means ior producing characters upon paper or similar substances which are invisible under ordinary circumstances and rendered A further object of the invention is the process by which is produced a sheet of paper or like material upon which has been spread material which'impregnates the fiber of the paper and becomes invisible under normal conditions and which, when Wet, becomes visible and remains so, so long as the paper is wet and becomes herein described and of the several steps makingpp said process and in the article resulting from the practice of the said process and the several steps, and which will be more particularly described hereinafter and pointed out in the claims.

' In carrying out the process forming the subjectmatter of this application, any approved sheet material may be employed, but preferably a paper known to the trade as water leaf paper and comprising a paper of open fibrous texture. Upon the paper so chosen is applied a waterproofing material which be-. comes invisible when properly treated, the said material being applied in any convenient manner as by the use of a pen, brush, stamp, or other marking or printing device to form letters, figures, pictures, or any desired characters upon the paper. While there may be various materials applicable to this process, I prefer to use phenol-phthalein dissolved in alcohol, the solution being neutral. The solution of phenol-phthalein may be any desired percentage relative to the alcohol, a very strong solution being less desirable for the reason that when applied to the paper it will show slightly upon the surface. The paper employed ispreferably white or cream and the phenol-phthalein solution, when applied and dried, is invisible upon such a surface. The

. phenol-phthalein solution may be dried by exposing to the atmosphere, but a very considerable time is required for drying under such conditions and it is preferably dried by inserting the impregnated sheet into an oven or like heating receptacle wherein artificial heat. may be applied. When the sheet thus impregnated has been thoroughly dried as described, the characters imprinted thereupon in the chemical are invisible and the sheet may be employed as ordinary blank paper and for any desired purpose.

After thoroughly drying the sheet it may be laid away, stored or shipped, any desired time intervening between the drying step of the process and the development of the characters. To develop the characters the sheet is simply wetted in any convenient and approved manncr, as by immersing in water, holding in vapor, spraying with water, wetting with a sponge or even with the tongue and when so wet, the paper which has not been impregnated becomes semi-transnatural opaque quality of the paper. So long as the surrounding paper remains wet and semi-transparent,

but when the paper has once more become dry the by repeating the wetting process. This development may be repeated several times without detracting materially from the clearness' with which the characters stand out upon the semi-transparent paper.

While phenol-phthalein has been described as a desirable chemical substance to produce the result mentioned, this application is not limited to the use of such chemical, but includes any and all chemical substances which render a fabric water proof by their application thereto and which become invisible upon the surface of the sheet when dry.

What I claim is ing a sheet with chemical characters invisible when dry andvisible when wet, of drying the sheet to render the chemical invisible, and wetting the sheet with water to develop the characters. I 2. The herein described process consisting in forming characters upon a sheet in a solution of phenol-phthalein dissolved in alcohol, of drying the sheet to render the characters invisible and wetting the sheet in water to develop the characters.

In testimony whereof I aiiix my signature in presence of two witnesses. 1

OTTO MEYER.

Witnesses:

DAVID MnAon WHITE, Grzonon B. WHITE.

parent, while the impregnated portions retain the the characters are easily discernible upon the surface,

1. The herein described process consisting in impregnat-.

characters again disappear and may be developed 

